The invention relates to an anode structure for a direct current arc furnace, and particularly to an anode constructed of electrically conducting refractory lining connected to a conductor on the outside of the furnace.
U.S. Pat. No. 4,541,099 discloses a direct current arc furnace with a bottom or hearth contact, in which the hearth or bottom lining of the furnace contains at its contacting face with the melt a ramming mass with electrically conductive metal parts or bricks with sheet metal inserts. To this is connected a first layer of electrically conductive bricks, a second layer of insulating bricks with interposed sheet metal layers or electrically conductive intermediate bricks and finally a third layer of electrically conductive bricks connected to connection contacts. This lining is dome-shaped or planar, it only being in contact with the melt in the bottom area. Quite apart from the fact that this bottom or hearth lining is very complicated and costly to produce, the current passing out from the central arc electrode is led away conically downwards. The areas in the vicinity of the furnace wall are consequently only inadequately supplied with heat, so that cold zones occur here.
U.S. Pat. No. 4,821,284 discloses the use of a steel billet projecting into the melt as the bottom or hearth electrode. In this case the effect of the downwardly directed arc occurs to an even greater extent, so that the arc cone is even more pointed and once again there are cold zones adjacent to the furnace wall. This electrode also requires a water cooling located below the molten metal bath. This causes problems from the safety standpoint.
In another direct current arc furnace known from U.S. Pat. No. 4,324,943 many small diameter metallic conductors are arranged over the entire hearth and are led inwards through the hearth wall. Although this avoids the cold zones in the vicinity of the wall, said distribution leads to concentrated small diameter wear of the refractory lining around the metallic conductors. Thus, dangerous thin points occur in the hearth area, which have to be regularly repaired.
Finally, U.S. Pat. No. 4,853,941 discloses a d.c. arc furnace in which, between a hearth electrode and the melt, is provided a unitary layer of electrically conductive refractory bricks. The bricks are made from a magnesite-graphite material which has been subject to a heart treatment in order to increase the electrical conductivity thereof. As hereagain the electrically conductive lining and the electrode are only positioned in the hearth area, cold zones on the furnace wall cannot be avoided. Moreover, the cooling conditions are unfavourable, so that the electrode is water-cooled.
The problem of the present invention is to provide an anode for a d.c. arc furnace, in which at least part of the furnace area receiving the melt is provided on its inside with an electrically conductive, refractory lining, which is electrically connected to a conductor located on the outside, which has a simple construction, ensures a uniform temperature distribution in the melt and also leads to a uniform wearing of the refractory lining. In addition, the need for water cooling is to be avoided.